1. Field of the Invention
The invention provides nucleotide sequences from coryneform bacteria which code for the metH gene and a process for the fermentative preparation of amino acids, in particular L-methionine, using bacteria in which the metH gene is enhanced.
2. Description of the Related Art
L-Amino acids, in particular L-methionine, are used in human medicine and in the pharmaceuticals industry, in the foodstuffs industry and very particularly in animal nutrition.
It is known that amino acids are prepared by fermentation from strains of coryneform bacteria, in particular Corynebacterium glutamicum. Because of their great importance, work is constantly being undertaken to improve the preparation process. Improvements to the process can relate to fermentation measures, such as, stirring and supply of oxygen, or to the composition of the nutrient media, such as, the sugar concentration during the fermentation, or to the working up of the product by, for example, ion exchange chromatography, or to the intrinsic output properties of the microorganism itself.
Methods of mutagenesis, selection and mutant selection are used to improve the output properties of these microorganisms. Strains which are resistant to antimetabolites, such as e.g. the methionine analogue α-methyl-methionine, ethionine, norleucine, N-acetylnorleucine, S-trifluoromethylhomocysteine, 2-amino-5-heprenoitic acid, seleno-methionine, methionine-sulfoximine, methoxine, 1-aminocyclopentane-carboxylic acid, or are auxotrophic for metabolites of regulatory importance and produce amino acids, such as e.g. L-methionine, are obtained in this manner.
Recombinant DNA techniques have also been employed for some years for improving Corynebacterium strains which produce L-amino acids, by amplifying individual amino acid biosynthesis genes and investigating their effect on the amino acid production.